Dielectrophersis Control of InAs based Nanowires for bio sensing

半导体器件越来越多地被用于基于医疗保健的传感器应用中，因为它们具有出色的能力，可以检测由于其电学和光学特性的变化而导致的周围环境的微小变化。最近，人们对半导体纳米线非常感兴趣，这些纳米线是从半导体表面垂直向上生长的，已经从一系列化合物半导体中展示了纳米线，包括砷化镓、磷化镓、砷化铟和铟锑。这些金属丝的生长要么是通过最初在表面沉积微小的金属液滴，要么是通过在氧化物掩模上形成纳米级的洞来启动的。得到的纳米线的长度可以超过1微米，直径可以低于100纳米。这些纳米线对生物传感和医疗保健应用特别感兴趣，原因有几个，首先，它们的小尺寸使其成为集成分子和其他光学和电子部件的理想选择。其次，由于导线的圆柱形，大部分电荷存在于表面，使它们对环境的变化特别敏感，例如，由于存在不同的生物标志物。然而，生长的垂直性质和由此产生的器件几何形状严重限制了这些纳米线的开发，因为纳米线通常被平面化并封装在聚合物层下。这导致了一个相对较大的最终器件，并也抑制了大部分表面电荷。这项拟议的工作为利用介电过程开发基于纳米线的传感器和设备提供了一种阶段性的改变。这是一个过程，在这个过程中，非均匀电场的作用会对带电粒子产生力。通过适当地控制电场，可以利用这一过程来精确地移动和定位粒子。为了实现这一点，纳米线将从其自然生长的衬底上移除，然后分散在溶剂中，然后进行介电泳将纳米线定位在预定的位置。这为进行纳米线生物传感和监测提供了一条诱人的途径，因为它能够直接将纳米线与微流体和其他光学或电气系统集成在一起，从而利用该技术提供的准确和可靠的定位。另一个优点是，通过该技术形成的纳米线设备可以以水平而不是垂直的配置实现。这将使与其他组件的集成变得更加直接，也使纳米线的整个表面能够与其环境相互作用，大大增强了纳米线对环境变化的敏感度。这些潜在的好处提供了极大地提高基于纳米线的传感器和器件的性能的可能性，以及能够以更高的效率和更低的成本制造。具体地说，该项目旨在通过介电泳法制造纳米线器件，建立工艺参数与最终器件的电、光和物理特性之间的关系，为可预测的器件制造开辟一条道路。最后，纳米线设备将与微流控系统集成，以演示离子流量传感器，允许在紧凑的实验室中通过芯片设备监控液体的浓度和流量。

Semiconductor devices are increasingly being utilized in healthcare based sensor applications due their excellent ability to detect minute changes in their surroundings due via alterations in their electrical and optical properties. Recently there has been much interest in semiconductor nanowires, these wires are grown vertically upwards from a semiconductor surface, with nanowires having been demonstrated from a range of compound semiconductors including, Gallium Arsenide, Gallium Phosphide, Indium Arsenide and Indium Antimony. Growth of these wires is initiated either by initially depositing tiny metal droplets on the surface or by forming nanoscale holes in an oxide mask. The resultant nanowires can have lengths in excess of 1um and diameters below 100nm.These nanowires are of particular interest for bio-sensing and healthcare applications for a number of reasons, firstly their small size makes them ideal to integrate molecules and other optical and electrical components. Secondly due to the cylindrical shape of the wires the majority of the charge resides on the surface making them especially sensitive to changes in their environment, for example arising from the presence of differing bio-markers. However the vertical nature of the growth and resultant device geometry severely limits the exploitation of these nanowires as the nanowires are routinely planarised and encapsulated under a polymer layer. This results in a relatively large final device and also supresses much of the surface charge. The proposed work here offers a step-change in the development of nanowire based sensors and devices by utilizing the process of dielectrophoresis. This is a process whereby the application of a non-uniform electric field results in a force upon a charged particle. By appropriately controlling the electric field it is possible to utilize this process to accurately move and position particles. To achieve this the nanowires will be removed from their native growth substrate and then dispersed in solvent before undergoing dielectrophoresis to position the wires at pre determined positions. This offers an attractive route to undertake nanowire bio-sensing and monitoring due to the ability to integrate the nanowires directly with microfluidics and other optical or electrical systems thus exploiting the accurate and reliable positioning offered by this technique.A further advantage is that nanowire devices formed via this technique can be achieved in a horizontal rather than vertical configuration. This will make integration with other components much more straightforward and also enable the whole surface of the nanowire to interact with its environment, greatly enhancing the sensitivity of the wires to any changes in their environment. These potential benefits offer the possibility to greatly enhance the performance of nanowire based sensors and devices as well as enabling to be fabricated more efficiently and at a reduced cost.Specifically this project aims to fabricate nanowire devices via dielectrophoresis, establishing relationships between the process parameters and the final devices electrical, optical and physical characteristics, opening a route for predictable device fabrication. Finally nanowire devices will be integrated with microfluidic systems to demonstrate an ionic flow sensor, allowing both the concentration and flow rate of liquids to be monitored in a compact lab on a chip device.